1. Field of the Invention
The present invention relates to an improved fuel injection nozzle for an internal combustion engine, in particular in a motor vehicle.
2. Description of the Prior Art
An injection nozzle of the type with which this invention is concerned is known, for example, from DE 100 58 153 A1 and has a first nozzle needle embodied in the form of a hollow needle and a second nozzle needle situated coaxial to the first nozzle needle. The first nozzle needle can control an injection of fuel through at least one first injection opening while the second nozzle needle can control the injection of fuel through at least one second injection opening. A control piston is provided for actuating the second nozzle needle and axially cooperates with the second nozzle needle or a second needle unit that includes the second nozzle needle. A control surface of this control piston oriented away from the injection openings is situated in a control chamber and can be acted by the control pressure prevailing therein. In a closed position of the second nozzle needle, the control piston rests axially against the second nozzle needle or second needle unit.
The first nozzle needle in the known injection nozzle can be directly controlled with the injection pressure, i.e. the first nozzle needle opens as soon as a sufficiently high injection pressure acts on a corresponding pressure shoulder of the first nozzle needle. If a fuel injection is to be executed only by means of the at least one first injection opening, then the control chamber is subjected to a correspondingly high control pressure so that the second nozzle needle remains closed. If a fuel injection is to also be executed by means of the at least one second injection opening, then the pressure in the control chamber is reduced until the injection pressure acting on a corresponding pressure shoulder on the second nozzle needle causes the second nozzle needle to open. The second nozzle needle is consequently controlled not by means of the injection pressure, but by means of the control pressure prevailing in the control chamber, which is also referred to as servo control. It is relatively expensive to implement a servo control this kind.